If you can pet them (and you don't have any sort of way to restrain them), scratch & rub their neck/shoulder area. Either side. Think a triangle shaped area.
After really scratching & rubbing, give a few heavy taps & slaps (not hard!). You don't want to spook, just get them ready. Then give the shot.
Cow hide is tough - you really have to be ready to push in the needle.
By now, your heifer knows what you did - you have to be quick & ready to make a tent in the skin (if you're giving sub c) or just in the neck if it's IM, insert needle, & push the plunger.
If she doesn't react when you insert the needle and you have time - you can pull back the plunger just a bit to make sure you don't have it in a vein.
Blood = vein. Pull out & try again.
We always give in the neck area so the meat isn't damaged. Some give along side the tail. ALso, we always get a bump for a few days to a week after the vacc.
http://extension.usu.edu/files/publi...H_Beef__40.pdf
Picture of where to give -
http://www.oklahomaclubcalfassociati.../Vaccinate.pdf